/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import java.io.Serializable;
import java.util.Collections;
import java.util.List;

import com.google.common.annotations.GwtCompatible;

/** An ordering that uses the natural order of the values. */
@GwtCompatible(serializable = true)
@SuppressWarnings({ "rawtypes", "unchecked" })
// TODO: the right way to explain this??
final class NaturalOrdering extends Ordering<Comparable> implements
        Serializable {
    static final NaturalOrdering INSTANCE = new NaturalOrdering();

    public int compare(Comparable left, Comparable right) {
        checkNotNull(right); // left null is caught later
        if (left == right) {
            return 0;
        }

        // we're permitted to throw CCE
        int result = left.compareTo(right);
        return result;
    }

    // TODO: the right way to explain this??
    @Override
    public <S extends Comparable> Ordering<S> reverse() {
        return (Ordering) ReverseNaturalOrdering.INSTANCE;
    }

    // Override to remove a level of indirection from inner loop
    // TODO: the right way to explain this??
    @Override
    public int binarySearch(List<? extends Comparable> sortedList,
            Comparable key) {
        return Collections.binarySearch((List) sortedList, key);
    }

    // Override to remove a level of indirection from inner loop
    @Override
    public <E extends Comparable> List<E> sortedCopy(Iterable<E> iterable) {
        List<E> list = Lists.newArrayList(iterable);
        Collections.sort(list);
        return list;
    }

    // preserving singleton-ness gives equals()/hashCode() for free
    private Object readResolve() {
        return INSTANCE;
    }

    @Override
    public String toString() {
        return "Ordering.natural()";
    }

    private NaturalOrdering() {
    }

    private static final long serialVersionUID = 0;
}
